Our prior U.S. Pat. No. 5,019,692, issued May 28, 1990 describes a problem in monitoring the surface of a roller in a heated pressure roller fuser. Typical contact monitors in such devices involve a thermistor embedded in or in contact with a carbon shoe that rides on the surface of the roller. The carbon shoe is used to reduce wear to both the roller surface and the sensing device. However, the carbon slides on the roller and both it and the roller wear. In our prior application we disclosed a roller sensing device in which a metallic roller rolls on the surface to be monitored and contains a variety of structures inside which monitors the temperature of the roller. This greatly reduces wear to both the heated roller and the sensing device.
Temperature control of heated roller fusers has always been adversely affected by any delay in response time of a device sensing the fusing surface. Delay in sensing temperature change causes the phenomena of "droop" and "overshoot" well known to those in the art.
U.S. Pat. No. 2,947,171, Peltola, issued Aug. 2, 1960, also shows a roller temperature sensing device containing a thermistor on the roller axis. This device requires full heating of the entire arrangement including heating of the air inside the roller to fully sense an increase in temperature. This aspect of its design adversely affects its response time.
It would be desirable to improve both the response time and the cost of these prior devices.